In a conventional pressure sensor (e.g., JP-A-2004-279327), a pressure sensor includes a sensor chip for outputting electric signals in accordance with a pressure received at a pressure receiving surface formed on one surface of the sensor chip, a first case having the sensor chip at a one end portion thereof, a second case mounted to the one end portion of the first case so that the sensor chip is covered, and a pressure introducing passage for introducing the pressure toward the sensor chip.
In this kind of pressure sensor, a pressure medium is introduced through the pressure introducing passage of the second case. The pressure receiving surface of the sensor chip formed in the first case receives the pressure, and the sensor chip outputs electric signals in accordance with the received pressure so that pressure detection is performed.
The pressure sensor can be used in a vehicle as pressure sensors for detecting a fuel pressure, a lubricating oil pressure for an engine or a driving system, a refrigerant pressure of an air conditioner and an exhaust gas pressure and so on.
In this case, the pressure medium such as the refrigerant of the air conditioner, the lubricating oil or the exhaust gas is directly introduced to the pressure receiving surface of the sensor chip or an electrically connection portion of the sensor chip of the pressure sensor.
When the pressure receiving surface of the sensor chip faces the pressure introducing passage, the pressure receiving surface is exposed directly to a flow of the pressure medium introduced through the passage. Therefore, foreign objects mixed in the pressure medium, such as dust, directly hit the pressure receiving surface. Also, contaminated materials also adhere to the pressure receiving surface. As a result, there is a possibility that the sensor chip properties are adversely affected.
The exposure of the electrically connection portion of the sensor chip to the pressure medium may induce deterioration of the sensor chip, such as corrosion, due to the pressure medium or the contaminated materials mixed therein.
Therefore, in the conventional pressure sensor described in JP-A-2004-279327, the sensor chip is covered with a metal diaphragm, and an oil, which is used as a pressure transmitting medium, is sealed within the meal diaphragm.
In this case, the sensor chip and the electrically connection portion are therefore protected from the pressure medium. At the same time the pressure of the pressure medium is received at the metal diaphragm and is transmitted to the sensor chip via the pressure transmitting medium.
Also, in another conventional pressure sensor, the sensor chip and electrodes of a base material are electrically connected by bumps, and the bumps and peripheries of the electrically connection portions of the electrodes are sealed with an adhesive material (e.g. JP-A-9-126920). According to this method, the electrically connection portion of the sensor chip is protected from being exposed to the pressure medium.
In this type of conventional pressure sensor, after the sensor chip and the electrodes of the base material are bonded via the bumps, the adhesive material is injected through gaps between the sensor chip and the base material towards the bumps, thereby a sealing of the electrically connection portion by the adhesive material is completed.
In order to reduce the size of the above-described pressure sensors, a structure of a pressure sensor, in which the metal diaphragm and the oil are eliminated, has been studied by the inventors of the present application.
This is because the shape and the size of the metal diaphragm affect considerably the sensor properties and it has been thought difficult to change the shape and size of the metal diaphragm. As a consequence, it has been difficult to reduce the size of the pressure sensor including the metal diaphragm in its structure.
More specifically, the larger the metal diaphragm becomes, the better a sensitivity of the metal diaphragm becomes, thereby the sensitivity of the sensor also improves. However, the size of the metal diaphragm cannot be made smaller in order to manufacture a more compact pressure sensor, especially in the radial direction (an equivalent direction to the radial direction of the diaphragm), due to the reasons explained as above.
Consequently, the elimination of the metal diaphragm and the oil has been tried. However, the sensor chip or the electrically connection portion of the sensor chip, which are not sufficient in environmental resistant, are exposed directly to the pressure medium, such as the refrigerant of the air conditioner, the lubricating oil or the exhaust gas when the metal diaphragm and the oil are eliminated.
Therefore, it is hard to maintain the sensor properties by simply eliminating the metal diaphragm and the oil, because the harmful effects are expected to the sensor chip and also to the electrically connection portion thereof.
In the conventional pressure sensor described in JP-A-2004-279327, the electrical connections of the sensor chip are made by bonding wires. When the bonding wires are used as electrically connecting members to the sensor chip, a space is required between connecting portions for the wire bonding process. As a result, it is not preferable in view of the compactness of the sensor, especially in the radial direction of the sensor.
Also, in the conventional pressure sensor described in JP-A-9-126920, the adhesive material is injected through the gaps between the sensor chip and the base material after the sensor chip and the base material are connected via the bumps. Therefore, the injection of the adhesive material may not be precisely performed around the bumps, and the connection portions by the bumps may be partially exposed by not being sealed properly.